Destro lock, personally. Might be slightly biased, but blowing people up with Chaosbolt and sniping low health people with Shadowburn and the pretty stupid self healing we are capable of in random BG's is just plain awesome.

And if you mean from scratch starting at level 1 then I still think Destro lock is pretty good. You don't get the Ember consuming toys till past level 42, but you could still put out some damage I guess + you'll always have Fear from level 14 onwards.

Starting from scratch. What class would you play for random battlegrounds?

Are we talking leveling through BGs and having fun?

In this case, go Mage. Shatter and Ice Barrier are brutal in low level PvP.

If we are talking about lvl 90 random BGs, then go hunter, mage or rogue. Hunters are pretty dominant in random BGs because they can sit back and nuke people. Most random BG players don't know how to fight ranged classes like hunters or mages that can slip away. Rogues will become dominant in 5.2 if the PTR changes go through. You just sit in stealth until you see some low hanging fruit and gank them with +50 energy, Marked for Death and Shadow Blades.

A druid gives you four different speccs allowing for a lot of versatility, at least ONE specc has always been overpowered or at least been very close to it. Currently has three fairly strong speccs for Arena/RBG and in general gives you the most for the smallest effort while being insanely easy to play.

Last time I checked, WoW had more than 4 classes.
I'm assuming something went wrong with the poll.

As it is not on the poll, I'd pick shaman.
I've been playing him the longest now, after druid in vanilla, hunter in tbc, then midway wotlk I changed to resto shammy, barely looked back. (only other competitor nowadays would be a rogue..I love stealth :P)

A druid gives you four different speccs allowing for a lot of versatility, at least ONE specc has always been overpowered or at least been very close to it. Currently has three fairly strong speccs for Arena/RBG and in general gives you the most for the smallest effort while being insanely easy to play.